The present invention relates to a charged-particle beam emitting device using a charged-particle beam such as an electron beam or ion beam. More particularly, it relates to a charged-particle beam emitting device and its optical-axis adjusting method which are preferable for acquiring a high-resolution image by suppressing a degradation in the image resolution even when the charged-particle beam is tilted on a sample.
In a charged-particle beam emitting device the representative of which is a scanning electron microscope, a narrowly converged charged-particle beam is scanned on a sample, thereby acquiring desired information (e.g., sample image) from the sample. In the charged-particle beam emitting device like this, implementation of high resolution has been in progress year by year. Simultaneously, in recent years, it has become necessary to tilt the charged-particle beam with respect to the sample so as to acquire tilted image of the sample.
In order to irradiate the sample with the charged-particle beam in the state of being tilted, there exists a method of utilizing the swing-back effect of the charged-particle beam in the off-axis of an objective lens. For example, in JP-U-55-48610 and JP-A-2-33843, the following method has been disclosed: The charged-particle beam is caused to enter the off-axis of the objective lens, thereby utilizing the converging effect (swing-back effect) of the objective lens. Also, in JP-A-2000-348658, the following technology has been disclosed: There is provided a two-stage deflecting unit for deflecting the charged-particle beam in mutually opposite directions within a converging magnetic field of the objective lens. This allows correction of transverse chromatic aberration which occurs when the charged-particle beam is tilted in the off-axis of the objective lens. Also, in JP-A-2001-15055, the following technology has been disclosed: A deflecting unit for causing the charged-particle beam to pass through the off-axis of the objective lens is provided on the electron-source closer side than the objective lens. Then, the chromatic aberration (transverse chromatic aberration) which occurs in the off-axis of the objective lens is corrected using a Wien filter which is provided on the electron-source closer side than the objective lens. This allows a reduction in the image-resolution degradation at the time when the charged-particle beam is tilted. Moreover, in WO 01/33603, the following technology has been disclosed: The Wien filter, which generates orthogonal electrostatic and electromagnetic fields in arbitrary two-dimensional directions orthogonal to the optical axis, is located on the optical axis on the electron-source closer side than the objective lens. This allows correction of the transverse chromatic aberration in an arbitrary direction.
In any one of the above-described conventional technologies, the charged-particle beam is tilted with respect to the sample by utilizing the swing-back effect of the beam in the off-axis of the objective lens. Meanwhile, in order to mutually cancel out aberrations which occur in the off-axes of a plurality of converging lenses including the objective lens, the following operation has been required: Namely, adjustment of an astigmatic corrector and adjustment of the optical axis are repeated, thereby driving the optical axis so that an image acquired turns out to become the sharpest one. This operation, however, requires significant amount of skill and experience. Accordingly, an axis adjusting method or axis adjusting function which is simpler and easier has been desired.